Casein kinase 2 as a potentially important enzyme in the nervous system

CK2 negatively regulates the extinction of remote fear memory

Cognitive behavioral therapy, rooted in exposure therapy, is currently the primary approach employed in the treatment of anxiety-related conditions, including post-traumatic stress disorder (PTSD). In laboratory settings, fear extinction in animals is a commonly employed technique to investigate exposure therapy; however, the precise mechanisms underlying fear extinction remain elusive. Casein kinase 2 (CK2), which regulates neuroplasticity via phosphorylation of its substrates, has a significant influence in various neurological disorders, such as Alzheimer's disease and Parkinson's disease, as well as in the process of learning and memory. In this study, we adopted a classical Pavlovian fear conditioning model to investigate the involvement of CK2 in remote fear memory extinction and its underlying mechanisms. The results indicated that the activity of CK2 in the medial prefrontal cortex (mPFC) of mice was significantly upregulated after extinction training of remote cued fear memory. Notably, administration of the CK2 inhibitor CX-4945 prior to extinction training facilitated the extinction of remote fear memory. In addition, CX-4945 significantly upregulated the expression of p-ERK1/2 and p-CREB in the mPFC. Our results suggest that CK2 negatively regulates remote fear memory extinction, at least in part, by inhibiting the ERK-CREB pathway. These findings contribute to our understanding of the underlying mechanisms of remote cued fear extinction, thereby offering a theoretical foundation and identifying potential targets for the intervention and treatment of PTSD.

Development of an efficient liposomal DOX delivery formulation for HCC therapy by targeting CK2α

Hepatocellular carcinoma (HCC) is a digestive tract cancer with high mortality and poor prognosis, especially in China. Current chemotherapeutic drugs lead to poor prognosis, low efficacy, and high side effects due to weak targeting specificity and rapidly formed multidrug resistance (MDR). Based on the previous studies on the doxorubicin (DOX) formulation for cancer targeting therapy, we developed a novel DOX delivery formulation for the targeting chemotherapy of HCC and DOX resistant HCC. HCSP4 was previously screened and casein kinase 2α (CK2α) was predicted as its specific target on HCC cells in our lab. In the study, miR125a-5p was firstly predicted as an MDR inhibiting miRNA, and then CK2α was validated as the target of HCSP4 and miR125a-5p using CK2α-/-HepG2 cells. Based on the above, an HCC targeting and MDR inhibiting DOX delivery liposomal formulation, HCSP4/Lipo-DOX/miR125a-5p was synthesized and tested for its HCC therapeutic efficacy in vitro. The results showed that the liposomal DOX delivery formulation targeted to HCC cells specifically and sensitively, and presented the satisfied therapeutic efficacy for HCC, particularly for DOX resistant HCC. The potential therapeutic mechanism of the DOX delivery formulation was explored, and the formulation inhibited the expression of MDR-relevant genes including ATP-binding cassette subfamily B member 1 (ABCB1, also known as P-glycoprotein), ATP-binding cassette subfamily C member 5 (ABCC5), enhancer of zeste homolog 2 (EZH2), and ATPase Na+/K+ transporting subunit beta 1 (ATP1B1). Our study presents a novel targeting chemotherapeutic drug formulation for the therapy of HCC, especially for drug resistant HCC, although it is primarily and needs further study in vivo, but provided a new strategy for the development of novel anticancer drugs.

Casein Kinase 2 Affects Epilepsy by Regulating Ion Channels: A Potential Mechanism

Epilepsy, characterized by recurrent seizures and abnormal brain discharges, is the third most common chronic disorder of the Central Nervous System (CNS). Although significant progress has been made in the research on antiepileptic drugs (AEDs), approximately one-third of patients with epilepsy are refractory to these drugs. Thus, research on the pathogenesis of epilepsy is ongoing to find more effective treatments. Many pathological mechanisms are involved in epilepsy, including neuronal apoptosis, mossy fiber sprouting, neuroinflammation, and dysfunction of neuronal ion channels, leading to abnormal neuronal excitatory networks in the brain. CK2 (Casein kinase 2), which plays a critical role in modulating neuronal excitability and synaptic transmission, has been shown to be associated with epilepsy. However, there is limited research on the mechanisms involved. Recent studies have suggested that CK2 is involved in regulating the function of neuronal ion channels by directly phosphorylating them or their binding partners. Therefore, in this review, we will summarize recent research advances regarding the potential role of CK2 regulating ion channels in epilepsy, aiming to provide more evidence for future studies.

Genetic analysis and literature review of a Poirier-Bienvenu neurodevelopmental syndrome family line caused by a de novo frameshift variant in CSNK2B

BACKGROUND

Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) is a rare autosomal dominant neurologic disorder caused by a heterozygous variant of CSNK2B, which is characterized by early onset epilepsy, hypotonia, varying degrees of intellectual disability (ID), developmental delay (DD), and facial dysmorphism. This study clarifies the molecular diagnosis and causative factors of a Chinese boy with POBINDS.

METHODS

The clinical phenotypes and ancillary laboratory tests were collected and analyzed by trio whole exome sequencing (WES) and copy number variant sequencing (CNV-seq) in the follow-up proband's families. The candidate variant was validated by Sanger sequencing and bioinformatics software was used to further explore the effect of the de novo frameshift variant on the protein structure.

RESULTS

The proband carries a de novo frameshift variant c.453_c.454insAC (p.H152fs*76) in CSNK2B. According to the ACMG genetic variant classification criteria and guidelines, the locus is a pathogenic variant (PVS1+PS2+PM2) and the associated disease was POBINDS. Protein structure prediction suggests significant differences in amino acid sequences before and after mutation.

CONCLUSION

A rare case of POBINDS caused by a novel frameshift variant in CSNK2B was diagnosed. The novel variant extends the variation spectrum of CSNK2B, which provides guidance for early clinical diagnosis, genetic counseling and treatment of this family. A review of the currently reported cases of POBINDS further enriches and summarizes the relationship between genotype and phenotype of POBINDS.

Quantitative proteomic and phosphoproteomic analyses of the hippocampus reveal the involvement of NMDAR1 signaling in repetitive mild traumatic brain injury

The cumulative damage caused by repetitive mild traumatic brain injury can cause long-term neurodegeneration leading to cognitive impairment. This cognitive impairment is thought to result specifically from damage to the hippocampus. In this study, we detected cognitive impairment in mice 6 weeks after repetitive mild traumatic brain injury using the novel object recognition test and the Morris water maze test. Immunofluorescence staining showed that p-tau expression was increased in the hippocampus after repetitive mild traumatic brain injury. Golgi staining showed a significant decrease in the total density of neuronal dendritic spines in the hippocampus, as well as in the density of mature dendritic spines. To investigate the specific molecular mechanisms underlying cognitive impairment due to hippocampal damage, we performed proteomic and phosphoproteomic analyses of the hippocampus with and without repetitive mild traumatic brain injury. The differentially expressed proteins were mainly enriched in inflammation, immunity, and coagulation, suggesting that non-neuronal cells are involved in the pathological changes that occur in the hippocampus in the chronic stage after repetitive mild traumatic brain injury. In contrast, differentially expressed phosphorylated proteins were mainly enriched in pathways related to neuronal function and structure, which is more consistent with neurodegeneration. We identified N-methyl-D-aspartate receptor 1 as a hub molecule involved in the response to repetitive mild traumatic brain injury , and western blotting showed that, while N-methyl-D-aspartate receptor 1 expression was not altered in the hippocampus after repetitive mild traumatic brain injury, its phosphorylation level was significantly increased, which is consistent with the omics results. Administration of GRP78608, an N-methyl-D-aspartate receptor 1 antagonist, to the hippocampus markedly improved repetitive mild traumatic brain injury-induced cognitive impairment. In conclusion, our findings suggest that N-methyl-D-aspartate receptor 1 signaling in the hippocampus is involved in cognitive impairment in the chronic stage after repetitive mild traumatic brain injury and may be a potential target for intervention and treatment.

MiR-93 alleviates DEHP plasticizer-induced neurotoxicity by negatively regulating TNFAIP1 and inhibiting ubiquitin-mediated degradation of CK2β

Di-(2-ethylhexyl) phthalate (DEHP) is a plasticizer that is widely used in various products, such as plastic packaging in food industries. As an environmental endocrine disruptor, it induces adverse effects on brain development and function. However, the molecular mechanisms by which DEHP induces learning and memory impairment remain poorly understood. Herein, we found that DEHP impaired learning and memory in pubertal C57BL/6 mice, decreased the number of neurons, downregulated miR-93 and the β subunit of casein kinase 2 (CK2β), upregulated tumor necrosis factor-induced protein 1 (TNFAIP1), and inhibited Akt/CREB pathway in mouse hippocampi. Coimmunoprecipitation and western blotting assays revealed that TNFAIP1 interacted with CK2β and promoted its degradation by ubiquitination. Bioinformatics analysis showed a miR-93 binding site in the 3'-untranslated region of Tnfaip1. A dual-luciferase reporter assay revealed that miR-93 targeted TNFAIP1 and negatively regulated its expression. MiR-93 overexpression prevented DEHP-induced neurotoxicity by downregulating TNFAIP1 and then activating CK2/Akt/CREB pathway. These data indicate that DEHP upregulates TNFAIP1 expression by downregulating miR-93, thus promoting ubiquitin-mediated degradation of CK2β, subsequently inhibiting Akt/CREB pathway, and finally inducing learning and memory impairment. Therefore, miR-93 can relieve DEHP-induced neurotoxicity and may be used as a potential molecular target for prevention and treatment of related neurological disorders.

An in silico approach to identify early damage biomarker candidates in metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare, autosomal recessive lysosomal storage disease. Deficient activity of arylsulfatase A causes sulfatides to accumulate in cells of different tissues, including those in the central and peripheral nervous systems, leading to progressive demyelination and neurodegeneration. Although there is some association between specific arylsulfatase A alleles and disease severity, genotype-phenotype correlations are not fully understood. We aimed to identify biomarker candidates of early tissue damage in MLD using a modeling approach based on systems biology. A review of the literature was performed in an initial disease characterization step, allowing identification of pathophysiological processes involved in MLD and proteins relating to these processes. Three mathematical models were generated to simulate different stages of MLD at the molecular level: an early pro-inflammatory stage model (including only processes considered to be active in the early stages of disease), a pre-demyelination stage model (including additional processes that are active after some disease progression), and a demyelination stage model (in which all pathophysiological processes are active). The models evaluated 3457 proteins of interest, individually and by pairs through data mining techniques, applying five filters to prioritize biomarkers that could differentiate between the models. Sixteen potential biomarkers were identified, including effectors relating to mitochondrial dysfunction, remyelination, and neurodegeneration. The findings were corroborated in a gene expression data set from T lymphocytes of patients with MLD; all candidates formed combinations that were able to distinguish patients with MLD from controls, and all but one candidate distinguished late-infantile MLD from juvenile MLD as part of a combinatorial biomarker pair. In particular, pro-neuregulin-1 appeared as differential on all comparisons (patients with MLD vs controls and within clinical subtypes); casein kinase II subunit alpha was detected as a potential individual marker within clinical subtypes. These findings provide a panel of biomarker candidates suitable for experimental validation and highlight the utility of mathematical models to identify biomarker candidates of early tissue damage in MLD with a high degree of accuracy and sensitivity.

CK2 inhibitor DMAT ameliorates spinal cord injury by increasing autophagy and inducing anti-inflammatory microglial polarization

Spinal cord injury (SCI) is a destructive and disabling nerve injury from which complete recovery has not yet been achieved due to complex pathology. Casein kinase II (CK2) is a pleiotropic serine/threonine protein kinase that plays an essential role in the nervous system. This study aimed to investigate the role of CK2 in SCI to understand the pathogenesis of SCI and explore new therapeutic methods. The SCI rat model of C5 unilateral clamp was established by modified clamp method in male adult SD rats. Then, CK2 inhibitor DMAT was used to treat SCI rats, and the behaviour, pathological changes in the spinal cord and microglial polarization were analysed. Additionally, the effects of DMAT on the polarization and autophagy of microglial BV-2 cells were investigated in vitro, and the effects of BV-2 polarization on spinal cord neuronal cells were analysed by Transwell coculture. Results showed that DMAT significantly increased the BBB score, improved histopathological injury, decreased the expression of inflammatory cytokines, and promoted M2 polarization of microglia in SCI rats. In vitro experiments further confirmed that DMAT could promote the polarization of BV-2 to the M2 type, promote autophagy, and reverse the LPS-induced decline in cell viability and increase in apoptosis of neuronal cells. The use of 3-MA confirmed that autophagy plays an important role in DMAT promoting M2 polarization of BV-2 to improve neuronal cell viability. In conclusion, CK2 inhibitor DMAT improved SCI by inducing anti-inflammatory polarization of microglia through autophagy and is a potential therapeutic target for SCI.

Haploinsufficiency as a Foreground Pathomechanism of Poirer-Bienvenu Syndrome and Novel Insights Underlying the Phenotypic Continuum of CSNK2B-Associated Disorders

CSNK2B encodes for the regulatory subunit of the casein kinase II, a serine/threonine kinase that is highly expressed in the brain and implicated in development, neuritogenesis, synaptic transmission and plasticity. De novo variants in this gene have been identified as the cause of the Poirier-Bienvenu Neurodevelopmental Syndrome (POBINDS) characterized by seizures and variably impaired intellectual development. More than sixty mutations have been described so far. However, data clarifying their functional impact and the possible pathomechanism are still scarce. Recently, a subset of CSNK2B missense variants affecting the Asp32 in the KEN box-like domain were proposed as the cause of a new intellectual disability-craniodigital syndrome (IDCS). In this study, we combined predictive functional and structural analysis and in vitro experiments to investigate the effect of two CSNK2B mutations, p.Leu39Arg and p.Met132LeufsTer110, identified by WES in two children with POBINDS. Our data prove that loss of the CK2beta protein, due to the instability of mutant CSNK2B mRNA and protein, resulting in a reduced amount of CK2 complex and affecting its kinase activity, may underlie the POBINDS phenotype. In addition, the deep reverse phenotyping of the patient carrying p.Leu39Arg, with an analysis of the available literature for individuals with either POBINDS or IDCS and a mutation in the KEN box-like motif, might suggest the existence of a continuous spectrum of CSNK2B-associated phenotypes rather than a sharp distinction between them.

Roles of Phosphorylation of N-Methyl-D-Aspartate Receptor in Chronic Pain

Phosphorylation of N-methyl-D-aspartate receptor (NMDAR) is widely regarded as a vital modification of synaptic function. Various protein kinases are responsible for direct phosphorylation of NMDAR, such as cyclic adenosine monophosphate-dependent protein kinase A, protein kinase C, Ca²⁺/calmodulin-dependent protein kinase II, Src family protein tyrosine kinases, cyclin-dependent kinase 5, and casein kinase II. The detailed function of these kinases on distinct subunits of NMDAR has been reported previously and contributes to phosphorylation at sites predominately within the C-terminal of NMDAR. Phosphorylation underlies both structural and functional changes observed in chronic pain, and studies have demonstrated that inhibitors of kinases are significantly effective in alleviating pain behavior in different chronic pain models. In addition, the exploration of drugs that aim to disrupt the interaction between kinases and NMDAR is promising in clinical research. Based on research regarding the modulation of NMDAR in chronic pain models, this review provides an overview of the phosphorylation of NMDAR-related mechanisms underlying chronic pain to elucidate molecular and pharmacologic references for chronic pain management.

CKII Control of Axonal Plasticity Is Mediated by Mitochondrial Ca2+ via Mitochondrial NCLX

Mitochondrial Ca²⁺ efflux by NCLX is a critical rate-limiting step in mitochondria signaling. We previously showed that NCLX is phosphorylated at a putative Casein Kinase 2 (CKII) site, the serine 271 (S271). Here, we asked if NCLX is regulated by CKII and interrogated the physiological implications of this control. We found that CKII inhibitors down-regulated NCLX-dependent Ca²⁺ transport activity in SH-SY5Y neuronal cells and primary hippocampal neurons. Furthermore, we show that the CKII phosphomimetic mutants on NCLX inhibited (S271A) and constitutively activated (S271D) NCLX transport, respectively, rendering it insensitive to CKII inhibition. These phosphomimetic NCLX mutations also control the allosteric regulation of NCLX by mitochondrial membrane potential (ΔΨm). Since the omnipresent CKII is necessary for modulating the plasticity of the axon initial segment (AIS), we interrogated, in hippocampal neurons, if NCLX is required for this process. Similarly to WT neurons, NCLX-KO neurons can exhibit homeostatic plasticity following M-channel block. However, while WT neurons utilize a CKII-sensitive distal relocation of AIS Na⁺ and Kv7 channels to decrease their intrinsic excitability, we did not observe such translocation in NCLX-KO neurons. Thus, our results indicate that NCLX is regulated by CKII and is a crucial link between CKII signaling and fast neuronal plasticity.

CK2 and protein kinases of the CK1 superfamily as targets for neurodegenerative disorders

Casein kinases are involved in a variety of signaling pathways, and also in inflammation, cancer, and neurological diseases. Therefore, they are regarded as potential therapeutic targets for drug design. Recent studies have highlighted the importance of the casein kinase 1 superfamily as well as protein kinase CK2 in the development of several neurodegenerative pathologies, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis. CK1 kinases and their closely related tau tubulin kinases as well as CK2 are found to be overexpressed in the mammalian brain. Numerous substrates have been detected which play crucial roles in neuronal and synaptic network functions and activities. The development of new substances for the treatment of these pathologies is in high demand. The impact of these kinases in the progress of neurodegenerative disorders, their bona fide substrates, and numerous natural and synthetic compounds which are able to inhibit CK1, TTBK, and CK2 are discussed in this review.

Casein Kinase 2 Signaling in White Matter Stroke

The growth of the aging population, together with improved stroke care, has resulted in an increase in stroke survivors and a rise in recurrent events. Axonal injury and white matter (WM) dysfunction are responsible for much of the disability observed after stroke. The mechanisms of WM injury are distinct compared to gray matter and change with age. Therefore, an ideal stroke therapeutic must restore neuronal and axonal function when applied before or after a stroke, and it must also protect across age groups. Casein kinase 2 (CK2), is expressed in the brain, including WM, and is regulated during the development and numerous disease conditions such as cancer and ischemia. CK2 activation in WM mediates ischemic injury by activating the Cdk5 and AKT/GSK3β signaling pathways. Consequently, CK2 inhibition using the small molecule inhibitor CX-4945 (Silmitasertib) correlates with preservation of oligodendrocytes, conservation of axon structure, and axonal mitochondria, leading to improved functional recovery. Remarkably, CK2 inhibition promotes WM function when applied after ischemic injury by specifically regulating the AKT/GSK3β pathways. The blockade of the active conformation of AKT confers post-ischemic protection to young and old WM by preserving mitochondria, implying AKT as a common therapeutic target across age groups. Using a NanoString nCounter miRNA expression profiling, comparative analyses of ischemic WM with or without CX-4945 treatment reveal that miRNAs are expressed at high levels in WM after ischemia, and CX-4945 differentially regulates some of these miRNAs. Therefore, we propose that miRNA regulation may be one of the protective actions of CX-4945 against WM ischemic injury. Silmitasertib is FDA approved and currently in use for cancer and Covid patients; therefore, it is plausible to repurpose CK2 inhibitors for stroke patients.

Evaluation of a Selective Chemical Probe Validates That CK2 Mediates Neuroinflammation in a Human Induced Pluripotent Stem Cell-Derived Microglial Model

Novel treatments for neurodegenerative disorders are in high demand. It is imperative that new protein targets be identified to address this need. Characterization and validation of nascent targets can be accomplished very effectively using highly specific and potent chemical probes. Human induced pluripotent stem cells (hiPSCs) provide a relevant platform for testing new compounds in disease relevant cell types. However, many recent studies utilizing this platform have focused on neuronal cells. In this study, we used hiPSC-derived microglia-like cells (MGLs) to perform side-by-side testing of a selective chemical probe, SGC-CK2-1, compared with an advanced clinical candidate, CX-4945, both targeting casein kinase 2 (CK2), one of the first kinases shown to be dysregulated in Alzheimer's disease (AD). CK2 can mediate neuroinflammation in AD, however, its role in microglia, the innate immune cells of the central nervous system (CNS), has not been defined. We analyzed available RNA-seq data to determine the microglial expression of kinases inhibited by SGC-CK2-1 and CX-4945 with a reported role in mediating inflammation in glial cells. As proof-of-concept for using hiPSC-MGLs as a potential screening platform, we used both wild-type (WT) MGLs and MGLs harboring a mutation in presenilin-1 (PSEN1), which is causative for early-onset, familial AD (FAD). We stimulated these MGLs with pro-inflammatory lipopolysaccharides (LPS) derived from E. coli and observed strong inhibition of the expression and secretion of proinflammatory cytokines by simultaneous treatment with SGC-CK2-1. A direct comparison shows that SGC-CK2-1 was more effective at suppression of proinflammatory cytokines than CX-4945. Together, these results validate a selective chemical probe, SGC-CK2-1, in human microglia as a tool to reduce neuroinflammation.

Protein Kinase CK2 Maintains Reciprocal Balance Between Th17 and Treg Cells in the Pathogenesis of UC

BACKGROUND

T helper 17 and regulatory T cells balance have crucial effects on the development of ulcerative colitis (UC). Currently, how to break this balance has not yet been found. Protein kinase CK2 is involved in the pathogenesis of immune-related disorders. However, its effects on the development of UC are obscure.

METHODS

The level of CK2 in the colonic tissues of UC patients was quantified by quantitative real-time polymerase chain reaction (qRT-PCR) and immune-histochemistry. Peripheral blood CD4+ T cells were treated with CK2 inhibitor CX4945 or transfected with Csnk2-interfering lentivirus; the mRNA expression and protein levels of inflammatory cytokines were detected by qRT-PCR, enzyme-linked immunosorbent assay, and flow cytometry. Moreover, CX4945 was administered to trinitrobenzene sulfonic acid (TNBS)-induced colitis mice model for determining the function of CK2 on the regulation of intestinal inflammation.

RESULTS

The CK2 level was markedly increased in inflamed mucosa of UC and highly expressed in CD4+ T cells. Blockade of CK2 by CX4945 inhibited Th17 but promoted regulatory T-cell (Treg) immune responses in CD4+ T cells from patients with UC. Moreover, CK2 blockade alleviated TNBS-induced colitis in mice. Inhibition of CK2 suppressed Th17 but promoted Treg differentiation by decreasing the phosphorylation level of signal transducer and activator of transcription (STAT) 3 and increasing the phosphorylation level of STAT5. The RNA-Seq and co-immunoprecipitation analysis further showed that CK2 could interact with Sirtuin 1 (SIRT1) and downregulate SIRT1 expression, which participated in Th17 inhibition but promoted Treg differentiation. Sirtuin 1 upregulation ameliorated TNBS-induced colitis, whereas SIRT1 blockade aggravated TNBS-induced colitis in mice.

CONCLUSIONS

CK2 have crucial effects on the development of UC by maintaining reciprocal balance between Th17 and Treg cells. Protein kinase CK2 blockade might be considered as a new therapeutic approach for UC treatment.

Comparing Two Neurodevelopmental Disorders Linked to CK2: Okur-Chung Neurodevelopmental Syndrome and Poirier-Bienvenu Neurodevelopmental Syndrome—Two Sides of the Same Coin?

In recent years, variants in the catalytic and regulatory subunits of the kinase CK2 have been found to underlie two different, yet symptomatically overlapping neurodevelopmental disorders, termed Okur-Chung neurodevelopmental syndrome (OCNDS) and Poirier-Bienvenu neurodevelopmental syndrome (POBINDS). Both conditions are predominantly caused by de novo missense or nonsense mono-allelic variants. They are characterized by a generalized developmental delay, intellectual disability, behavioral problems (hyperactivity, repetitive movements and social interaction deficits), hypotonia, motricity and verbalization deficits. One of the main features of POBINDS is epilepsies, which are present with much lower prevalence in patients with OCNDS. While a role for CK2 in brain functioning and development is well acknowledged, these findings for the first time clearly link CK2 to defined brain disorders. Our review will bring together patient data for both syndromes, aiming to link symptoms with genotypes, and to rationalize the symptoms through known cellular functions of CK2 that have been identified in preclinical and biochemical contexts. We will also compare the symptomatology and elaborate the specificities that distinguish the two syndromes.

Structural and Enzymological Evidence for an Altered Substrate Specificity in Okur-Chung Neurodevelopmental Syndrome Mutant CK2αLys198Arg

Specific de novo mutations in the CSNK2A1 gene, which encodes CK2α, the catalytic subunit of protein kinase CK2, are considered as causative for the Okur-Chung neurodevelopmental syndrome (OCNDS). OCNDS is a rare congenital disease with a high phenotypic diversity ranging from neurodevelopmental disabilities to multi-systemic problems and characteristic facial features. A frequent OCNDS mutation is the exchange of Lys198 to Arg at the center of CK2α′s P+1 loop, a key element of substrate recognition. According to preliminary data recently made available, this mutation causes a significant shift of the substrate specificity of the enzyme. We expressed the CK2α^Lys198Arg recombinantly and characterized it biophysically and structurally. Using isothermal titration calorimetry (ITC), fluorescence quenching and differential scanning fluorimetry (Thermofluor), we found that the mutation does not affect the interaction with CK2β, the non-catalytic CK2 subunit, and that the thermal stability of the protein is even slightly increased. However, a CK2α^Lys198Arg crystal structure and its comparison with wild-type structures revealed a significant shift of the anion binding site harboured by the P+1 loop. This observation supports the notion that the Lys198Arg mutation causes an alteration of substrate specificity which we underpinned here with enzymological data.

Expanding Phenotype of Poirier–Bienvenu Syndrome: New Evidence from an Italian Multicentrical Cohort of Patients

Background: Poirier–Bienvenu Neurodevelopmental Syndrome (POBINDS) is a rare disease linked to mutations of the CSNK2B gene, which encodes for a subunit of caseinkinase CK2 involved in neuronal growth and synaptic transmission. Its main features include early-onset epilepsy and intellectual disability. Despite the lack of cases described, it appears that POBINDS could manifest with a wide range of phenotypes, possibly related to the different mutations of CSNK2B. Methods: Our multicentric, retrospective study recruited nine patients with POBINDS, detected using next-generation sequencing panels and whole-exome sequencing. Clinical, laboratory, and neuroimaging data were reported for each patient in order to assess the severity of phenotype, and eventually, a correlation with the type of CSNK2B mutation. Results: We reported nine unrelated patients with heterozygous de novo mutations of the CSNK2B gene. All cases presented epilepsy, and eight patients were associated with a different degree of intellectual disability. Other features detected included endocrinological and vascular abnormalities and dysmorphisms. Genetic analysis revealed six new variants of CSNK2B that have not been reported previously. Conclusion: Although it was not possible to assess a genotype–phenotype correlation in our patients, our research further expands the phenotype spectrum of POBINDS patients, identifying new mutations occurring in the CSNK2B gene.

Characterizing the role of the dark kinome in neurodegenerative disease - A mini review

BACKGROUND

Drugs that modulate previously unexplored targets could potentially slow or halt the progression of neurodegenerative diseases. Several candidate proteins lie within the dark kinome, those human kinases that have not been well characterized. Much of the kinome (~80%) remains poorly studied, and these targets likely harbor untapped biological potential.

SCOPE OF REVIEW

This review highlights the significance of kinases as mediators of aberrant pathways in neurodegeneration and provides examples of published high-quality small molecules that modulate some of these kinases.

MAJOR CONCLUSIONS

There is a need for continued efforts to develop high-quality chemical tools to illuminate the function of understudied kinases in the brain. Potent and selective small molecules enable accurate pairing of an observed phenotype with a protein target.

GENERAL SIGNIFICANCE

The examples discussed herein support the premise that validation of therapeutic hypotheses surrounding kinase targets can be accomplished via small molecules and they can serve as the basis for disease-focused drug development campaigns.

The hypervariable region of atlastin-1 is a site for intrinsic and extrinsic regulation

Atlastin (ATL) GTPases catalyze homotypic membrane fusion of the peripheral endoplasmic reticulum (ER). GTP-hydrolysis–driven conformational changes and membrane tethering are prerequisites for proper membrane fusion. However, the molecular basis for regulation of these processes is poorly understood. Here we establish intrinsic and extrinsic modes of ATL1 regulation that involve the N-terminal hypervariable region (HVR) of ATLs. Crystal structures of ATL1 and ATL3 exhibit the HVR as a distinct, isoform-specific structural feature. Characterizing the functional role of ATL1’s HVR uncovered its positive effect on membrane tethering and on ATL1’s cellular function. The HVR is post-translationally regulated through phosphorylation-dependent modification. A kinase screen identified candidates that modify the HVR site specifically, corresponding to the modifications on ATL1 detected in cells. This work reveals how the HVR contributes to efficient and potentially regulated activity of ATLs, laying the foundation for the identification of cellular effectors of ATL-mediated membrane processes.

Atypic SUMOylation of Nor1/NR4A3 regulates neural cell viability and redox sensitivity

Neuron-derived orphan receptor 1, NR4A3 (Nor1)/NR4A3 is an orphan nuclear receptor involved in the transcriptional control of developmental and neurological functions. Oxidative stress-induced conditions are primarily associated with neurological defects in humans, yet the impact on Nor1-mediated transcription of neuronal genes remains with unknown mechanism. Here, we demonstrate that Nor1 is a non-conventional target of SUMO2/3 conjugation at Lys-137 contained in an atypic ψKxSP motif referred to as the pSuM. Nor1 pSuM SUMOylation differs from the canonical process with the obligate phosphorylation of Ser-139 by Ras signaling to create the required negatively charged interface for SUMOylation. Additional phosphorylation at sites flanking the pSuM is also mediated by the coordinated action of protein kinase casein kinase 2 to function as a small ubiquitin-like modifier enhancer, regulating Nor1-mediated transcription and proteasomal degradation. Nor1 responsive genes involved in cell proliferation and metabolism, such as activating transcription factor 3, cyclin D1, CASP8 and FADD-like apoptosis regulator, and enolase 3 were upregulated in response to pSuM disruption in mouse HT-22 hippocampal neuronal cells and human neuroblastoma SH-SY5Y cells. We also identified critical antioxidant genes, such as catalase, superoxide dismutase 1, and microsomal glutathione S-transferase 2, as responsive targets of Nor1 under pSuM regulation. Nor1 SUMOylation impaired gene transcription through less effective Nor1 chromatin binding and reduced enrichment of histone H3K27ac marks to gene promoters. These effects resulted in decreased neuronal cell growth, increased apoptosis, and reduced survival to oxidative stress damage, underlying the role of pSuM-modified Nor1 in redox homeostasis. Our findings uncover a hierarchical post-translational mechanism that dictates Nor1 non-canonical SUMOylation, disrupting Nor1 transcriptional competence, and neuroprotective redox sensitivity.

Clinical and genetic analysis of six Chinese children with Poirier-Bienvenu neurodevelopmental syndrome caused by CSNK2B mutation

Mutations in CSNK2B lead to Poirier-Bienvenu neurodevelopmental syndrome (POBINDS), a rare neurodevelopmental disorder. Only 14 cases of POBINDS have been reported worldwide. The main manifestations are seizures, often tonic-clonic, with or without intellectual disability, growth retardation, and developmental language retardation. We conducted a comprehensive phenotypic mining and trio-whole exome sequencing on six children with POBINDS for gene diagnosis and analyzed the different variants using bioinformatics analysis software and related experiments. This paper reviews previous literature and discusses two common missense variants that lead to structural changes. Among the six patients, four, one, and one had tonic-clonic, myoclonic, and febrile seizures, respectively. Language development disorder, motor development disorder, and developmental delay/intellectual disability (DD/ID) are the main clinical features. All children had de novo mutations in CSNK2B, including three missense variants (c.410G > T/p.(Cys137Phe), c.494A > G/p.(His165Arg), and c.3G > A/p.(Met1Ile)), two splice variants (c.292-2A > T, c.558-3 T > G), and one frameshift variant (c.499delC/p.(Leu167Serfs*60)). Three missense variants were predicted to be harmful by various software programs, and two splicing variants were found to produce new exonic splicing enhancers by the minigene assay. Western blot analysis showed that the frameshift variant resulted in decreased protein expression. According to a literature review, c.3G > A/p.(Met1Ile), c.292-2A > T, c.558-3 T > G, and c.499delC/p.(Leu167Serfs*60) are novel variants of CSNK2B. The decrease or loss of protein function caused by CSNK2B mutations may be a pathogenic factor in this cohort. The severity of the POBINDS phenotype differs, and refractory epilepsy may be accompanied by a more serious DD/ID, language disorder, and motor retardation. At present, there is no specific treatment, and antiepileptic therapy usually requires the combination of two or more anti-epileptic drugs.

Beyond Antioxidant Effects: Nature-Based Templates Unveil New Strategies for Neurodegenerative Diseases

The complex network of malfunctioning pathways occurring in the pathogenesis of neurodegenerative diseases (NDDs) represents a huge hurdle in the development of new effective drugs to be used in therapy. In this context, redox reactions act as crucial regulators in the maintenance of neuronal microenvironment homeostasis. Particularly, their imbalance results in the severe compromising of organism’s natural defense systems and subsequently, in the instauration of deleterious OS, that plays a fundamental role in the insurgence and progress of NDDs. Despite the huge efforts in drug discovery programs, the identification process of new therapeutic agents able to counteract the relentless progress of neurodegenerative processes has produced low or no effective therapies. Consequently, a paradigm-shift in the drug discovery approach for these diseases is gradually occurring, paving the way for innovative therapeutical approaches, such as polypharmacology. The aim of this review is to provide an overview of the main pharmacological features of most promising nature-based scaffolds for a possible application in drug discovery, especially for NDDs, highlighting their multifaceted effects against OS and neuronal disorders.

Adenosine Signaling and Clathrin-Mediated Endocytosis of Glutamate AMPA Receptors in Delayed Hypoxic Injury in Rat Hippocampus: Role of Casein Kinase 2

Chronic adenosine A1R stimulation in hypoxia leads to persistent hippocampal synaptic depression, while unopposed adenosine A2AR receptor stimulation during hypoxia/reperfusion triggers adenosine-induced post-hypoxia synaptic potentiation (APSP) and increased neuronal death. Still, the mechanisms responsible for this adenosine-mediated neuronal damage following hypoxia need to be fully elucidated. We tested the hypothesis that A1R and A2AR regulation by protein kinase casein kinase 2 (CK2) and clathrin-dependent endocytosis of AMPARs both contribute to APSPs and neuronal damage. The APSPs following a 20-min hypoxia recorded from CA1 layer of rat hippocampal slices were abolished by A1R and A2AR antagonists and by broad-spectrum AMPAR antagonists. The inhibitor of GluA2 clathrin-mediated endocytosis Tat-GluA2-3Y peptide and the dynamin-dependent endocytosis inhibitor dynasore both significantly inhibited APSPs. The CK2 antagonist DRB also inhibited APSPs and, like hypoxic treatment, caused opposite regulation of A1R and A2AR surface expression. APSPs were abolished when calcium-permeable AMPAR (CP-AMPAR) antagonist (IEM or philanthotoxin) or non-competitive AMPAR antagonist perampanel was applied 5 min after hypoxia. In contrast, perampanel, but not CP-AMPAR antagonists, abolished APSPs when applied during hypoxia/reperfusion. To test for neuronal viability after hypoxia, propidium iodide staining revealed significant neuroprotection of hippocampal CA1 pyramidal neurons when pretreated with Tat-GluA2-3Y peptide, CK2 inhibitors, dynamin inhibitor, CP-AMPAR antagonists (applied 5 min after hypoxia), and perampanel (either at 5 min hypoxia onset or during APSP). These results suggest that the A1R-CK2-A2AR signaling pathway in hypoxia/reperfusion injury model mediates increased hippocampal synaptic transmission and neuronal damage via calcium-permeable AMPARs that can be targeted by perampanel for neuroprotective stroke therapy.

[Effect of etimizole structural analogues on protein kinase CK2, protein phosphorylation and transcription of chromatin in rat brain cortex and hippocampus]

Protein kinase CK2 is an important enzyme in the nervous system. The nuclear forms of CK2 regulate chromatin structure and gene expression, the key processes for long-term memory formation. Memory modulators, the Structural Analogues of Etimizole (SAE), were able to increase or decrease the activity of chromatin-associated CK in the cortex and hippocampus of rat brain in vitro. In vivo memory enhancers from SAE-group (3 mg/kg) stimulated CK2 activity and the transcriptional ability of chromatin in the cortex and hippocampus, starting from 30 min with a peak for 60 min and a duration up to 180 min. At these periods the memory inhibitor from the SAE-group reduced CK2 activity and chromatin transcription. It is assumed that the modulating effect of SAE on CK2 activity and transcription underlies the effects of these compounds on long-term memory.

Synthesis and SAR of Tetracyclic Inhibitors of Protein Kinase CK2 Derived from Furocarbazole W16

The serine/threonine kinase CK2 modulates the activity of more than 300 proteins and thus plays a crucial role in various physiological and pathophysiological processes including neurodegenerative disorders of the central nervous system and cancer. The enzymatic activity of CK2 is controlled by the equilibrium between the heterotetrameric holoenzyme CK2α₂β₂ and its monomeric subunits CK2α and CK2β. A series of analogues of W16 ((3aR,4S,10S,10aS)‐4‐{[(S)‐4‐benzyl‐2‐oxo‐1,3‐oxazolidin‐3‐yl]carbonyl}‐10‐(3,4,5‐trimethoxyphenyl)‐4,5,10,10a‐tetrahydrofuro[3,4‐b]carbazole‐1,3(3aH)‐dione ((+)‐3  a)) was prepared in an one‐pot, three‐component Levy reaction. The stereochemistry of the tetracyclic compounds was analyzed. Additionally, the chemically labile anhydride structure of the furocarbazoles 3 was replaced by a more stable imide (9) and N‐methylimide (10) substructure. The enantiomer (−)‐3  a (K_i=4.9 μM) of the lead compound (+)‐3  a (K_i=31 μM) showed a more than sixfold increased inhibition of the CK2α/CK2β interaction (protein‐protein interaction inhibition, PPII) in a microscale thermophoresis (MST) assay. However, (−)‐3  a did not show an increased enzyme inhibition of the CK2α₂β₂ holoenzyme, the CK2α subunit or the mutated CK2α′ ^C336S subunit in the capillary electrophoresis assay. In the pyrrolocarbazole series, the imide (−)‐9  a (K_i=3.6 μM) and the N‐methylimide (+)‐10  a (K_i=2.8 μM) represent the most promising inhibitors of the CK2α/CK2β interaction. However, neither compound could inhibit enzymatic activity. Unexpectedly, the racemic tetracyclic pyrrolocarbazole (±)‐12, with a carboxy moiety in the 4‐position, displays the highest CK2α/CK2β interaction inhibition (K_i=1.8 μM) of this series of compounds.

Germline de novo variants in CSNK2B in Chinese patients with epilepsy

CSNK2B, which encodes the beta subunit of casein kinase II (CK2), plays an important role in neuron morphology and synaptic transmission. Variants in CSNK2B associated with epilepsy and/or intellectual disability (ID)/developmental delay (DD) have been reported in five cases only. Among the 816 probands suspected hereditary epilepsy whose initial report of trio-based whole exome sequencing (WES) were negative, 10 de novo pathogenic or likely pathogenic variants of CSNK2B in nine probands were identified after reanalysis of their raw Trio-WES data. Six of the nine epileptic patients had ID/DD. The age of seizure onset of these nine patients with CSNK2B variants ranged from 2–12 months. Eight patients had age of seizure onset of less than 6 months. The epilepsy of most probands (8/9) was generalized tonic-clonic seizure and clustered (6/9). Most patients had normal electroencephalogram (5/9) and brain magnetic resonance image (7/9) results. Most patients (7/9) had easy-to-control seizures. Levetiracetam was the most commonly used drug in seizure-free patients (5/7). The variants detected in five patients (5/9, 55.6%) were located in the zinc-binding domain. In summary, our research provided evidence that variants in CSNK2B are associated with epilepsy with or without ID/DD. CSNK2B-related epilepsy is relatively easy to be controlled. The zinc-binding domain appears to be the hotspot region for mutation.

Protein Kinase CK2 Subunits Differentially Perturb the Adhesion and Migration of GN11 Cells: A Model of Immature Migrating Neurons

Protein kinase CK2 (CK2) is a highly conserved and ubiquitous kinase is involved in crucial biological processes, including proliferation, migration, and differentiation. CK2 holoenzyme is a tetramer composed by two catalytically active (α/α’) and two regulatory (β) subunits and exerts its function on a broad range of targets. In the brain, it regulates different steps of neurodevelopment, such as neural differentiation, neuritogenesis, and synaptic plasticity. Interestingly, CK2 mutations have been recently linked to neurodevelopmental disorders; however, the functional requirements of the individual CK2 subunits in neurodevelopment have not been yet investigated. Here, we disclose the role of CK2 on the migration and adhesion properties of GN11 cells, an established model of mouse immortalized neurons, by different in vitro experimental approaches. Specifically, the cellular requirement of this kinase has been assessed pharmacologically and genetically by exploiting CK2 inhibitors and by generating subunit-specific CK2 knockout GN11 cells (with a CRISPR/Cas9-based approach). We show that CK2α’ subunit has a primary role in increasing cell adhesion and reducing migration properties of GN11 cells by activating the Akt-GSK3β axis, whereas CK2α subunit is dispensable. Further, the knockout of the CK2β regulatory subunits counteracts cell migration, inducing dramatic alterations in the cytoskeleton not observed in CK2α’ knockout cells. Collectively taken, our data support the view that the individual subunits of CK2 play different roles in cell migration and adhesion properties of GN11 cells, supporting independent roles of the different subunits in these processes.

CK2 inhibition protects white matter from ischemic injury

Strokes occur predominantly in the elderly and white matter (WM) is injured in most strokes, contributing to the disability associated with clinical deficits. Casein kinase 2 (CK2) is expressed in neuronal cells and was reported to be neuroprotective during cerebral ischemia. Recently, we reported that CK2 is abundantly expressed by glial cells and myelin. However, in contrast to its role in cerebral (gray matter) ischemia, CK2 activation during ischemia mediated WM injury via the CDK5 and AKT/GSK3β signaling pathways (Bastian et al., 2018). Subsequently, CK2 inhibition using the small molecule inhibitor CX-4945 correlated with preservation of oligodendrocytes as well as conservation of axon structure and axonal mitochondria, leading to improved functional recovery. Notably, CK2 inhibition promoted WM function when applied before or after ischemic injury by differentially regulating the CDK5 and AKT/GSK3β pathways. Specifically, blockade of the active conformation of AKT conferred post-ischemic protection to young, aging, and old WM, suggesting a common therapeutic target across age groups. CK2 inhibitors are currently being used in clinical trials for cancer patients; therefore, it is important to consider the potential benefits of CK2 inhibitors during an ischemic attack.

CK2 inhibition confers functional protection to young and aging axons against ischemia by differentially regulating the CDK5 and AKT signaling pathways

White matter (WM) is injured in most strokes, which contributes to functional deficits during recovery. Casein kinase 2 (CK2) is a protein kinase that is expressed in brain, including WM. To assess the impact of CK2 inhibition on axon recovery following oxygen glucose deprivation (OGD), mouse optic nerves (MONs), which are pure WM tracts, were subjected to OGD with or without the selective CK2 inhibitor CX-4945. CX-4945 application preserved axon function during OGD and promoted axon function recovery when applied before or after OGD. This protective effect of CK2 inhibition correlated with preservation of oligodendrocytes and conservation of axon structure and axonal mitochondria. To investigate the pertinent downstream signaling pathways, siRNA targeting the CK2α subunit identified CDK5 and AKT as downstream molecules. Consequently, MK-2206 and roscovitine, which are selective AKT and CDK5 inhibitors, respectively, protected young and aging WM function only when applied before OGD. However, a novel pan-AKT allosteric inhibitor, ARQ-092, which targets both the inactive and active conformations of AKT, conferred protection to young and aging axons when applied before or after OGD. These results suggest that AKT and CDK5 signaling contribute to the WM functional protection conferred by CK2 inhibition during ischemia, while inhibition of activated AKT signaling plays the primary role in post-ischemic protection conferred by CK2 inhibition in WM independent of age. CK2 inhibitors are currently being used in clinical trials for cancer patients; therefore, our results will provide rationale for repurposing these drugs as therapeutic options for stroke patients by adding novel targets.

CK2 Phosphorylating I2PP2A/SET Mediates Tau Pathology and Cognitive Impairment

Casein kinase 2 (CK2) is highly activated in Alzheimer disease (AD) and is associated with neurofibrillary tangles formation. Phosphorylated SET, a potent PP2A inhibitor, mediates tau hyperphosphorylation in AD. However, whether CK2 phosphorylates SET and regulates tau pathological phosphorylation in AD remains unclear. Here, we show that CK2 phosphorylating SET at Ser9 induced tau hyperphosphorylation in AD. We found that either Aβ treatment or tau overexpression stimulated CK2 activation leading to SET Ser9 hyperphosphorylation in neurons and animal models, while inhibition of CK2 by TBB abolished this event. Overexpression of CK2 in mouse hippocampus via virus injection induced cognitive deficit associated with SET Ser9 hyperphosphorylation. Injection of SET Ser9 phosphorylation mimetic mutant induced tau pathology and behavior impairments. Conversely co-injection of non-phosphorylated SET S9A with CK2 abolished the CK2 overexpression-induced AD pathology and cognitive deficit. Together, our data demonstrate that CK2 phosphorylates SET at Ser9 leading to SET cytoplasmic translocation and inhibition of PP2A resulting in tau pathology and cognitive impairments.

Comprehensive integrative analyses identify GLT8D1 and CSNK2B as schizophrenia risk genes

Recent genome-wide association studies (GWAS) have identified multiple risk loci that show strong associations with schizophrenia. However, pinpointing the potential causal genes at the reported loci remains a major challenge. Here we identify candidate causal genes for schizophrenia using an integrative genomic approach. Sherlock integrative analysis shows that ALMS1, GLT8D1, and CSNK2B are schizophrenia risk genes, which are validated using independent brain expression quantitative trait loci (eQTL) data and integrative analysis method (SMR). Consistently, gene expression analysis in schizophrenia cases and controls further supports the potential role of these three genes in the pathogenesis of schizophrenia. Finally, we show that GLT8D1 and CSNK2B knockdown promote the proliferation and inhibit the differentiation abilities of neural stem cells, and alter morphology and synaptic transmission of neurons. These convergent lines of evidence suggest that the ALMS1, CSNK2B, and GLT8D1 genes may be involved in pathophysiology of schizophrenia.

More than 100 risk loci for schizophrenia have been identified by genome-wide association studies. Here, the authors apply an integrative genomic approach to prioritize risk genes and validate GLT8D1 and CSNK2B as candidate causal genes by in vitro studies in neural stem cells.

Adenosine A1 and A2A Receptors in the Brain: Current Research and Their Role in Neurodegeneration

The inhibitory adenosine A1 receptor (A1R) and excitatory A2A receptor (A2AR) are predominantly expressed in the brain. Whereas the A2AR has been implicated in normal aging and enhancing neurotoxicity in multiple neurodegenerative diseases, the inhibitory A1R has traditionally been ascribed to have a neuroprotective function in various brain insults. This review provides a summary of the emerging role of prolonged A1R signaling and its potential cross-talk with A2AR in the cellular basis for increased neurotoxicity in neurodegenerative disorders. This A1R signaling enhances A2AR-mediated neurodegeneration, and provides a platform for future development of neuroprotective agents in stroke, Parkinson’s disease and epilepsy.

Selected flavonoid compounds as promising inhibitors of protein kinase CK2α and CK2α', the catalytic subunits of CK2

CK2 is a ubiquitous protein kinase involved in many cell functions. During the last years it became an interesting target in cancer research. A series of flavonoid compounds was tested as inhibitors of protein kinase CK2. Several substances were found to be highly active against both catalytic subunits with IC₅₀ values below 1 μM in case of CK2α'. The most promising inhibitor we identified is chrysoeriol with IC₅₀ values of 250 and 34 nM for CK2α and CK2α', respectively.

Protein kinase CK2 modulates HSJ1 function through phosphorylation of the UIM2 domain

HSJ1 (DNAJB2), a member of the DNAJ family of molecular chaperones, is a key player in neuronal proteostasis maintenance. It binds ubiquitylated proteins through its Ubiquitin Interacting Motifs (UIMs) and facilitates their delivery to the proteasome for degradation. Mutations in the DNAJB2 gene lead to inherited neuropathies such as Charcot-Marie-Tooth type-2, distal hereditary motor neuropathies, spinal muscular atrophy with parkinsonism and the later stages can resemble amyotrophic lateral sclerosis. HSJ1 overexpression can reduce aggregation of neurodegeneration-associated proteins in vitro and in vivo; however, the regulation of HSJ1 function is little understood. Here we show that CK2, a ubiquitous and constitutively active protein kinase, phosphorylates HSJ1 within its second UIM, at the dominant site Ser250 and the hierarchical site Ser247. A phospho-HSJ1 specific antibody confirmed phosphorylation of endogenous HSJ1a and HSJ1b. A tandem approach of phospho-site mutation and treatment with CK2 specific inhibitors demonstrated that phosphorylation at these sites is accompanied by a reduced ability of HSJ1 to bind ubiquitylated clients and to exert its chaperone activity. Our results disclose a novel interplay between ubiquitin- and phosphorylation-dependent signalling, and represent the first report of a regulatory mechanism for UIM-dependent function. They also suggest that CK2 inhibitors could release the full neuroprotective potential of HSJ1, and deserve future interest as therapeutic strategies for neurodegenerative disease.

CK2-An Emerging Target for Neurological and Psychiatric Disorders

Protein kinase CK2 has received a surge of attention in recent years due to the evidence of its overexpression in a variety of solid tumors and multiple myelomas as well as its participation in cell survival pathways. CK2 is also upregulated in the most prevalent and aggressive cancer of brain tissue, glioblastoma multiforme, and in preclinical models, pharmacological inhibition of the kinase has proven successful in reducing tumor size and animal mortality. CK2 is highly expressed in the mammalian brain and has many bona fide substrates that are crucial in neuronal or glial homeostasis and signaling processes across synapses. Full and conditional CK2 knockout mice have further elucidated the importance of CK2 in brain development, neuronal activity, and behavior. This review will discuss recent advances in the field that point to CK2 as a regulator of neuronal functions and as a potential novel target to treat neurological and psychiatric disorders.

The New Role for an Old Kinase: Protein Kinase CK2 Regulates Metal Ion Transport

The pleiotropic serine/threonine protein kinase CK2 was the first kinase discovered. It is renowned for its role in cell proliferation and anti-apoptosis. The complexity of this kinase is well reflected by the findings of past decades in terms of its heterotetrameric structure, subcellular location, constitutive activity and the extensive catalogue of substrates. With the advent of non-biased high-throughput functional genomics such as genome-wide deletion mutant screening, novel aspects of CK2 functionality have been revealed. Our recent discoveries using the model organism Saccharomyces cerevisiae and mammalian cells demonstrate that CK2 regulates metal toxicity. Extensive literature search reveals that there are few but elegant works on the role of CK2 in regulating the sodium and zinc channels. As both CK2 and metal ions are key players in cell biology and oncogenesis, understanding the details of CK2’s regulation of metal ion homeostasis has a direct bearing on cancer research. In this review, we aim to garner the recent data and gain insights into the role of CK2 in metal ion transport.

Protein kinase CK2 in development and differentiation

Among the human kinomes, protein kinase CK2 (formerly termed casein kinase II) is considered to be essential, as it is implicated in the regulation of various cellular processes. Experiments with pharmacological inhibitors of the kinase activity of CK2 provide evidence that CK2 is essential for development and differentiation. Therefore, the present review addresses the role of CK2 during embryogenesis, neuronal, adipogenic, osteogenic and myogenic differentiation in established model cell lines, and in embryonic, neural and mesenchymal stem cells. CK2 kinase activity appears to be essential in the early stages of differentiation, as CK2 inhibition at early time points generally prevents differentiation. In addition, the present review reports on target proteins of CK2 in embryogenesis and differentiation.

Protein kinase CK2 regulates metal toxicity in neuronal cells

Protein kinase CK2 is a pleiotropic tetrameric enzyme, regulating numerous biological processes from cell proliferation to stress response. This study demonstrates for the first time that CK2 is involved in the regulation of metal uptake and toxicity in neuronal cells. After the determination of inhibitory concentrations (IC50) for a range of metal salts (ZnSO4, Al(mal)3, CoCl2, CrO3, NaAsO2 and CaCl2) in Neuro-2a mouse neuroblastoma cells, the effect of CK2 on metal toxicity was investigated by three lines of experiments using CK2 inhibitors, metal ion specific fluorophores and siRNA-mediated knockdown of CK2 expression. The results showed that both CK2 inhibitors, 4,5,6,7-tetrabromobenzotriazole (TBB) and quinalizarin, markedly reduced the toxicity of Zn(ii), Al(iii), Co(ii), Cr(vi) and As(iii). Confocal microscopy imaging revealed that Zn(ii) uptake was accompanied by the increase of intracellular Ca(ii) in Neuro-2a cells treated with IC50 of ZnSO4 (240 μM), and such concurrent elevation of intracellular Zn(ii) and Ca(ii) was blocked by TBB and quinalizarin. The role of CK2 in metal uptake was further characterised using specific siRNA against each of the three subunits (CK2α, α' and β) and the data demonstrate that CK2α' is the prominent subunit regulating the metal toxicity. Finally, the role of CK2 in metal toxicity was found to be conserved in the distant species-Saccharomyces cerevisiae by employing the complete deletion mutants of CK2 (cka1Δ, cka2Δ, ckb1Δ and ckb2Δ). Taken together, these findings shed light on a new facet of CK2 functionality and provide a basis for further research on the regulation of Zn(ii) and Ca(ii) homeostasis by CK2.

Follicle-Stimulating Hormone (FSH)-dependent Regulation of Extracellular Regulated Kinase (ERK) Phosphorylation by the Mitogen-activated Protein (MAP) Kinase Phosphatase MKP3

Within the ovarian follicle, granulosa cells (GCs) surround and support immature oocytes. FSH promotes the differentiation and proliferation of GCs and is essential for fertility. We recently reported that ERK activation is necessary for FSH to induce key genes that define the preovulatory GC. This research focused on the phosphoregulation by FSH of ERK within GCs. FSH-stimulated ERK phosphorylation on Thr(202)/Tyr(204) was PKA-dependent, but MEK(Ser(217)/Ser(221)) phosphorylation was not regulated; rather, MEK was already active. However, treatment of GCs with the EGF receptor inhibitor AG1478, a dominant-negative RAS, an Src homology 2 domain-containing Tyr phosphatase inhibitor (NSC 87877), or the MEK inhibitor PD98059 blocked FSH-dependent ERK(Thr(202)/Tyr(204)) phosphorylation, demonstrating the requirement for upstream pathway components. We hypothesized that FSH via PKA enhances ERK phosphorylation by inhibiting the activity of a protein phosphatase that constitutively dephosphorylates ERK in the absence of FSH, allowing MEK-phosphorylated ERK to accumulate in the presence of FSH because of inactivation of the phosphatase. GCs treated with different phosphatase inhibitors permitted elimination of both Ser/Thr and Tyr phosphatases and implicated dual specificity phosphatases (DUSPs) in the dephosphorylation of ERK. Treatment with MAP kinase phosphatase (MKP3, DUSP6) inhibitors increased ERK(Thr(202)/Tyr(204)) phosphorylation in the absence of FSH to levels comparable with ERK phosphorylated in the presence of FSH. ERK co-immunoprecipitated with Myc-FLAG-tagged MKP3(DUSP6). GCs treated with MKP3(DUSP6) inhibitors blocked and PKA inhibitors enhanced dephosphorylation of recombinant ERK2-GST in an in vitro phosphatase assay. Together, these results suggest that FSH-stimulated ERK activation in GCs requires the PKA-dependent inactivation of MKP3(DUSP6).

Increased occurrence of protein kinase CK2 in astrocytes in Alzheimer's disease pathology

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease. In addition to the occurrence of amyloid deposits and widespread tau pathology, AD is associated with a neuroinflammatory response characterized by the activation of microglia and astrocytes. Protein kinase 2 (CK2, former casein kinase II) is involved in a wide variety of cellular processes. Previous studies on CK2 in AD showed controversial results, and the involvement of CK2 in neuroinflammation in AD remains elusive.

METHODS

In this study, we used immunohistochemical and immunofluorescent staining methods to investigate the localization of CK2 in the hippocampus and temporal cortex of patients with AD and non-demented controls. We compared protein levels with Western blotting analysis, and we investigated CK2 activity in human U373 astrocytoma cells and human primary adult astrocytes stimulated with IL-1β or TNF-α.

RESULTS

We report increased levels of CK2 in the hippocampus and temporal cortex of AD patients compared to non-demented controls. Immunohistochemical analysis shows CK2 immunoreactivity in astrocytes in AD and control cases. In AD, the presence of CK2 immunoreactive astrocytes is increased. CK2 immunopositive astrocytes are associated with amyloid deposits, suggesting an involvement of CK2 in the neuroinflammatory response. In U373 cells and human primary astrocytes, the selective CK2 inhibitor CX-4945 shows a dose-dependent reduction of the IL-1β or TNF-α induced MCP-1 and IL-6 secretion.

CONCLUSIONS

This data suggests that CK2 in astrocytes is involved in the neuroinflammatory response in AD. The reduction in pro-inflammatory cytokine secretion by human astrocytes using the selective CK2 inhibitor CX-4945 indicates that CK2 could be a potential target to modulate neuroinflammation in AD.

Microtubule Dynamics in Neuronal Development, Plasticity, and Neurodegeneration

Neurons are the basic information-processing units of the nervous system. In fulfilling their task, they establish a structural polarity with an axon that can be over a meter long and dendrites with a complex arbor, which can harbor ten-thousands of spines. Microtubules and their associated proteins play important roles during the development of neuronal morphology, the plasticity of neurons, and neurodegenerative processes. They are dynamic structures, which can quickly adapt to changes in the environment and establish a structural scaffold with high local variations in composition and stability. This review presents a comprehensive overview about the role of microtubules and their dynamic behavior during the formation and maturation of processes and spines in the healthy brain, during aging and under neurodegenerative conditions. The review ends with a discussion of microtubule-targeted therapies as a perspective for the supportive treatment of neurodegenerative disorders.

The intracellular domain of L1CAM binds to casein kinase 2α and is neuroprotective via inhibition of the tumor suppressors PTEN and p53

Cell adhesion molecule L1 promotes neuritogenesis and neuronal survival through triggering MAPK pathways. Based on the findings that L1 is associated with casein kinase 2 (CK2), and that deficiency in PTEN promotes neuritogenesis in vitro and regeneration after trauma, we examined the functional relationship between L1 and PTEN. In parallel, we investigated the tumor suppressor p53, which also regulates neuritogenesis. Here, we report that the intracellular domain of L1 binds to the subunit CK2α, and that knockdown of L1 leads to CK2 dephosphorylation and an increase in PTEN and p53 levels. Overexpression of L1, but not the L1 mutants L1 (S1181N, E1184V), which reduced binding between L1 and CK2, reduced expression levels of PTEN and p53 proteins, and enhanced levels of phosphorylated CK2α and mammalian target of rapamycin, which is a downstream effector of PTEN and p53. Treatment of neurons with a CK2 inhibitor or transfection with CK2α siRNA increased levels of PTEN and p53, and inhibited neuritogenesis. The combined observations indicate that L1 downregulates expression of PTEN and p53 via direct binding to CK2α. We suggest that L1 stimulates neuritogenesis by activating CK2α leading to decreased levels of PTEN and p53 via a novel, L1-triggered and CK2α-mediated signal transduction pathway. L1CAM (L1 cell adhesion molecule) is implicated in neural functions through the cognate src/MAP kinase signaling pathway. We now describe a novel signaling platform operating via the alpha subunit of casein kinase 2 which binds to the intracellular domain of L1. Knockdown of L1CAM leads to increased levels of tumor suppressor PTEN (phosphatase and tensin homolog) and p53, known to inhibit neuritogenesis in vitro and recovery from trauma in vivo. By activating this enzyme, L1CAM adds to its beneficial functions by decreasing the levels of PTEN and p53.

CK2 Secreted by Leishmania braziliensis Mediates Macrophage Association Invasion: A Comparative Study between Virulent and Avirulent Promastigotes

CK2 is a protein kinase distributed in different compartments of Leishmania braziliensis: an externally oriented ecto-CK2, an intracellular CK2, and a secreted CK2. This latter form is constitutively secreted from the parasite (CsCK2), but such secretion may be highly enhanced by the association of specific molecules, including enzyme substrates, which lead to a higher enzymatic activity, called inductively secreted CK2 (IsCK2). Here, we examined the influence of secreted CK2 (sCK2) activity on the infectivity of a virulent L. braziliensis strain. The virulent strain presented 121-fold higher total CK2 activity than those found in an avirulent strain. The use of specific CK2 inhibitors (TBB, DRB, or heparin) inhibited virulent parasite growth, whereas no effect was observed in the avirulent parasites. When these inhibitors were added to the interaction assays between the virulent L. braziliensis strain and macrophages, association index was drastically inhibited. Polyamines enhanced sCK2 activity and increased the association index between parasites and macrophages. Finally, sCK2 and the supernatant of the virulent strain increased the association index between the avirulent strain and macrophages, which was inhibited by TBB. Thus, the kinase enzyme CK2 seems to be important to invasion mechanisms of L. braziliensis.

Casein kinase: the triple meaning of a misnomer

The term 'casein kinase' has been widely used for decades to denote protein kinases sharing the ability to readily phosphorylate casein in vitro. These fall into three main classes: two of them, later renamed as protein kinases CK1 (casein kinase 1, also known as CKI) and CK2 (also known as CKII), are pleiotropic members of the kinome functionally unrelated to casein, whereas G-CK, or genuine casein kinase, responsible for the phosphorylation of casein in the Golgi apparatus of the lactating mammary gland, has only been identified recently with Fam20C [family with sequence similarity 20C; also known as DMP-4 (dentin matrix protein-4)], a member of the four-jointed family of atypical protein kinases, being responsible for the phosphorylation of many secreted proteins. In hindsight, therefore, the term 'casein kinase' is misleading in every instance; in the case of CK1 and CK2, it is because casein is not a physiological substrate, and in the case of G-CK/Fam20C/DMP-4, it is because casein is just one out of a plethora of its targets, and a rather marginal one at that. Strikingly, casein kinases altogether, albeit representing a minimal proportion of the whole kinome, appear to be responsible for the generation of up to 40-50% of non-redundant phosphosites currently retrieved in human phosphopeptides database. In the present review, a short historical explanation will be provided accounting for the usage of the same misnomer to denote three unrelated classes of protein kinases, together with an update of our current knowledge of these pleiotropic enzymes, sharing the same misnomer while playing very distinct biological roles.

Casein kinase II regulates N-methyl-D-aspartate receptor activity in spinal cords and pain hypersensitivity induced by nerve injury

Increased N-methyl-d-aspartate receptor (NMDAR) activity and phosphorylation in the spinal cord are critically involved in the synaptic plasticity and central sensitization associated with neuropathic pain. However, the mechanisms underlying increased NMDAR activity in neuropathic pain conditions remain poorly understood. Here we show that peripheral nerve injury induces a large GluN2A-mediated increase in NMDAR activity in spinal lamina II, but not lamina I, neurons. However, NMDAR currents in spinal dorsal horn neurons are not significantly altered in rat models of diabetic neuropathic pain and resiniferatoxin-induced painful neuropathy (postherpedic neuralgia). Inhibition of protein tyrosine kinases or protein kinase C has little effect on NMDAR currents potentiated by nerve injury. Strikingly, casein kinase II (CK2) inhibitors normalize increased NMDAR currents of dorsal horn neurons in nerve-injured rats. In addition, inhibition of calcineurin, but not protein phosphatase 1/2A, augments NMDAR currents only in control rats. CK2 inhibition blocks the increase in spinal NMDAR activity by the calcineurin inhibitor in control rats. Furthermore, nerve injury significantly increases CK2α and CK2β protein levels in the spinal cord. In addition, inhibition of CK2 or CK2β knockdown at the spinal level substantially reverses pain hypersensitivity induced by nerve injury. Our study indicates that neuropathic pain conditions with different etiologies do not share the same mechanisms, and increased spinal NMDAR activity is distinctly associated with traumatic nerve injury. CK2 plays a prominent role in the potentiation of NMDAR activity in the spinal dorsal horn and may represent a new target for treatments of chronic pain caused by nerve injury.